Cyclization alkenyl epoxides

The tributyltin radical adds to the alkenyl epoxide 3 to give an alkoxy radical intermediate. Hydrogen atom abstraction (1,5-H shift) then gives a new radical a- to the benzyloxy group. This radical can cyclize onto the alkene, with concommitant release... 

Alkenyl epoxides have been analogously used in the synthesis of bicyclic compounds [69]. Addition of a thiyl radical to a suitably protected epoxyketone enolate generated the oxiranyl carbinyl radical which initiated a cascade of uni-molecular steps (i.e. ring-opening, 1,5-radical translocation, 5-exo cyclization, and ejection of the PhS radical) to produce the final enol product in good yield and high diastereoselectivity (equation (31)). The PhS radical-induced fragmentation of alkenyl epoxy silanes has been found to afford a-trimethylsilyl aldehydes [70]. 

The preparation of 2,3,5-trisubstituted 4,5-dihydrofurans 81 with complete regio-control can be realized by an one-pot transformation involving epoxidation of 2-alkenyl-1,3-dicarbonyls by in situ generated dimethyldioxirane, and is followed by a S-exo-ieX intramolecular nucleophilic cyclization under the same basic condition <00TL10127>. 

VO(acac)2/TBHP CATALYZED EPOXIDATION OF 2-(2-ALKENYL)PHENOLS. HIGHLY REGIO- AND DIASTEREOSELECTIVE OXIDATIVE CYCLIZATION TO 2,3-DIHYDROBENZOFURANOLS AND 3-CHROMANOLS... 

The procedures are very easy to reproduce and the mild and catalytic conditions are far superior to previously employed m-CPBA ", to perform, respectively, the epoxidation and the oxidative cyclization of 2-(2-alkenyl)phenols. 

Several alkenyl hydroperoxides have been successfully cyclized to five-, six- and seven-membered ring peroxides (equation 241).38s 388 Alkaline sodium borohydride reduction of these mercurials is frequently accompanied by epoxide or cyclic ether formation. 

Only one example was found where this class of amino acids was produced. Oxidation of 7.246 gave a ketone and treatment with boron trifluoride led to the conjugated ketone, 7.247.132 Conjugate addition of azide, reduction to the amine and cyclization gave diastereomeric methyl 9-(3-hexyl-2-aziridino)nonanoic acid (J.248 and 7.249). The final step in that sequence proceeded in only 37% yield. If the alkenyl moiety was converted to an epoxide moiety, aziridine carboxylic acids were prepared in good yield, via the azide.132... 

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